January in the UK is normally quite cold, so this time of year is great for starting your seeds indoors. If you have a garage or polytunnel or space in your house. You can start planting those plants that will be ready to go out when the time starts getting a little warmer. I find that it works out cheaper than buying my plants from the garden centre.
In this vlog I go through some of the plants I recommend you could successfully start off indoors. To then transplant when the season changes. My list is by no means exhaustive, so feel free to add your own ideas to what I present here.
Seeds to sow in January
I have started cayenne pepper, turnips, cauliflower, asparagus, mixed lettuce, collard and even sweet potatoes. I used disposable plastic cups as a propagator, rather than throw them away after use. I recycle them and use them for my gardening.